1. Field of the Invention
The invention relates to a process for preparing emulsions of highly viscous organopolysiloxanes. The invention further relates to emulsions of highly viscous organopolysiloxanes.
2. Description of the Related Art
For the preparation of polysiloxanes having high viscosity, a series of methods exists, which are based mainly on condensation reactions. For instance, a standard method is to prepare silanol-functional highly viscous polysiloxanes from low-viscosity hydrolysates of the chlorosilanes, usually dimethyldichlorosilane, by condensing them to form water at relatively high temperature, usually under the action of acidic catalysts. Such condensations proceed only slowly and incompletely in aqueous emulsion, such that an increase in viscosity of the siloxane raw materials used only occurs to a modest degree. This method cannot be used at all for the preparation of emulsions of highly viscous amine oils.
In a similar manner, silanol-functional polysiloxanes can be condensed with methoxysilanes to form methanol. For this purpose, relatively high temperatures and catalysts are usually required in order to achieve industrially acceptable conversion rates. For instance, the standard process for preparing amino-functional siloxanes typical for the market is the base-catalysed condensation of aminoalkyl methoxysilanes with a short-chain hydrolysate of dimethyldichlorosilane at elevated temperature.
In view of the reaction temperatures of 100° C. and higher, and the reaction time over several hours, this process for preparing emulsions of highly viscous polysiloxanes is unsuitable, particularly when the continuous phase of the emulsion is water. In this case, it is in fact possible in principle for relatively highly viscous organopolysiloxanes first to be prepared and then be emulsified. Depending on the mechanical design, the emulsification process itself is limited to oils with not too high a viscosity such that organopolysiloxanes with more than 50,000 mPa·s at 25° C. can scarcely be emulsified with acceptable properties, and an economically viable procedure requires products with, if anything, less than 30,000 mPa·s viscosity at 25° C.
DE-A 2500020 describes a process for preparing aminosiloxanes, in which silanol-terminated polysiloxanes are reacted with α-aminosilanes which bear an alkoxy group. The reaction proceeds at moderate temperatures with elimination of alcohol. However, it is only possible with this technique to prepare comparatively unstable α-aminosiloxanes and also only in difunctional telechelic form.
Highly viscous polysiloxanes can also be obtained by polyaddition reactions, as described in U.S. Pat. No. 5,241,034 and U.S. Pat. No. 6,252,100. EP-A 874 017 and U.S. Pat. No. 6,451,909 disclose polyaddition reactions in emulsion for the preparation of highly viscous polysiloxanes. However, it is common to all of these polyaddition methods that metal catalysts are required for the progress of the reaction and are often undesired. In the presence of N-containing sil(ox)anes, inhibition effects also occur, so that it is barely possible, if at all, to carry out an efficiently catalysed polyaddition.